1) Field of the Invention
The instant invention is one of those devices that serves to facilitate the implantation of artificial hip prostheses into the long leg bone of human beings.
Invariably, the primary difficulty with total hip joint replacement procedures as currently performed by orthopaedic surgeons is the tendency of such devices once implanted in human bone to loosen in-situ with the passage of time. For patients who are confronted with such a phenomenon, the choice is simple though unpalatable, namely corrective surgery to be performed in order to alleviate the perambulatory and other problems such as pain and/or discomfort that result from such loosening. It has been demonstrated through studies that there is as much as a 40% loosening rate with respect to such devices per roughly ten year terms of implantation. For reasons that will soon be articulated in more detail, the instant invention serves to markedly militate against such loosening thereby alleviating the eventual need on the part of such patients for such corrective surgery.
Currently, when artificial hip prostheses are implanted into the femoral bones of patients, methyl methacrylate is utilized as a bonding agent in order to bond to the prostheses and at the same time to bond to the bone being implanted to thereby hold the prostheses to such bone. The bonding agent functions to accomplish fixation by way of adherence to an implanted prosthesis and by way of penetration of the interstitial cavitations within such bone structure while in a semi-liquid or gelatinous state such that when it hardens or cures, there is then a basis for such prosthesis fixation to such bone. Briefly stated, the femoral head and top portion of a patient's' femoral bone are surgically excised away from the bone. Then a canal or shaft is bored into the bone, then the canal or shaft is filled with gelatinous methyl methacrylate, then a hip prosthesis with an artificial femoral head of its own is pressed down into the cement filled canal or shaft and found to be relatively firmly in place once said cement hardens. The cement itself is delivered into the shaft under pressure by way of syringe-like gun screwed at its base into a rigid hollow applicator tube. Once the shaft is filled with cement, a spongy tarp is placed over the filled shaft and pressure is applied down on the tarp by the surgeon in an attempt to pack the cement tightly into the shaft and hopefully ultimately into the many small interstitial cavitations lining the boundaries of the shaft.
The primary problem with respect to such loosening as referred to above lies in the bond of cement to bone by way of such cement eventually weakening with the passage of time. The integrity of such bonding is subject to the inevitability of bone growth dynamics. Bone is a living tissue and hence changes its size and shape over time thus actuating the possibility of loosening at the interstitial cavitations into which such cement would have originally been placed change in respect of size and shape. Certain steps have been incorporated into a generally accepted hip replacement surgical protocol in order to combat such a problem. One such step has been the one whereby such cement in its gelatinous state is centrifuged prior to application in order to berid the cement to the greatest possible extent of air vacuoles within it that themselves operate to compromise to no small extent the integrity of the initial bond of such cement to the bone formed by way of such cement's filling of such interstitial cavitations within such bone upon application as such. Moreover, a restrictor cap is placed at the bottom of the shaft prior to filling the shaft in order to prevent the cement from seeping into distal part of the femur at the base of the shaft. Finally tamping down on the bonding cement, as noted above, with a spongy tarp once the shaft is completely filled is yet another precaution taken to hopefully alleviate potential loosening. However, as will be noted with an eye toward the foregoing, notwithstanding such advances in respect of surgical protocol, as matters currently stand in respect of the art of inserting such prostheses into bone, except as respects the success in such regard enjoyed by your inventor with resort to the utilization of his Biomedical Cement Bonding Enhancer as otherwise taught in U.S. Pat. No. 5,468,245 entitled, A Biomedical Cement Bonding Enhancer, no effort in view of the same is now able to be made to markedly minimize such loosening by way of isolating the injected gelatinous cement from air and an inexorable creation of porosity by such air within such cement that adversely affects bonding at the boundaries of the shaft and indeed even within the cement itself in terms of its relative density, also a factor in respect of such loosening until, at last, at least, the above-mentioned spongy tarp is applied.
The instant applicator tube on the other hand, embodies a markedly revolutionary departure from the foregoing art and for reasons that will now be set forth, is indeed, respectfully submitted, new, unique and unquestionably useful. Once a femoral shaft has been bored and a syringe unit is attached to the instant applicator tub after having been filled with gelatinous cement, the instant applicator tube is then inserted into the shaft to a distance of two centimeters or so above a previously inserted resistor cap. The cement is then introduced into the shaft out of the lower end of the instant applicator tube below the level of the circular tip component portion of the instant applicator tube. Such an undertaking causes such injected cement, previously rendered relatively free of air vacuoles and now exposed to virtually no air, to ooze under pressure laterally, much deeper than would have previously been the case with regards to the protocol previously outlined, into the interstitial cavitations within such bone located at the lateral inner boundary of the shaft. Such deeper oozing actuates the potential for much more dependable bonding upon hardening notwithstanding bone growth dynamics over time. Injection into the closed space within the shaft just below the base of the circular shaped flexible tip component of the instant invention to the extent that such tip causes much greater penetration of the interstitial cavitations and hence much greater bone-cement bonding, due to the great increase in local pressure caused by the creation of such a closed space by and in view of the presence of the tip. Greater intra-cement bonding and concomitantly enhanced density absent the potential for the erstwhile creation of air vacuoles, within the cement itself will, once again, be found as well. This much more effective bonding greatly minimizes to a marked degree any potential propensity for eventual loosening. Withdrawal back another two centimeters in distance is followed by more cement being injected into a new enclosed space between the base of the tip and the top surface of the just previously injected cement, and the process is repeated until at last the shaft is filled as tightly as possible with such now relatively air tight gelatinous cement. The applicator tube is removed from the shaft, the spongy tarp is applied to the top layer of the cement, the prosthesis is then firmly inserted into the cement filled shaft and the cement is left to harden thereby resulting in the very firm positioning of a prosthesis so anchored to bone as to most likely markedly minimize any potential propensity for eventual prosthesis loosening.
The means by which the instant device functions so effectively in respect of the foregoing lies in the fact that the circular shaped flexible tip component of the instant applicator tube upon insertion of the tube affixed to the end of a syringe creates a tightly closed shaft space into which cement can be introduced. The tip at its edging adheres firmly to the walling of the shaft thereby creating a succession of airtight subspaces all the while the cement is being injected after successive withdrawals up the shaft. The advantage of the instant invention over the above-mentioned Biomedical Cement Bonding Enhancer, lies in its relative simplicity and concomitantly lower cost of manufacture.
2) Prior Art
Your inventor is not aware of any prior art that anticipates the claims contemplated by the instant invention.